Systems and apparatus relating to diffusers in combustion turbine engines

ABSTRACT

A discharge diffuser that includes: a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity; an inner diffuser wall that defines an inner radial flowpath of the upstream section; and an outer diffuser wall that defines an outer radial flowpath of the upstream section; wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.

BACKGROUND OF THE INVENTION

This present application relates generally to turbine diffuser design, which, as used herein and unless specifically stated otherwise, is meant to include all types of combustion turbine or rotary engines, including gas turbine engines, aircraft engines, and others. More specifically, but not by way of limitation, the present application relates to turbine diffuser design providing robust diffuser and CDC performance.

In general, a turbine engine includes a compressor that delivers a supply of highly compressed air to a combustor for combustion with a fuel. The resulting flow of hot gases from the combustor drives the turbines from which work may be extracted. Turbine engines may be configured with an axial compressor that is mechanically coupled by a common shaft or rotor to a downstream turbine, with a combustor positioned between the compressor and the turbine. Air leaves the compressor with a relatively high velocity and, conventionally, a diffuser is utilized for initially decreasing the velocity of the compressed airflow and minimizing subsequent pressure losses. The diffuser may include splitter vanes that divide the airflow into separate diffuser passages. A diffuser dump region or cavity receives airflow from the diffuser, and further deceleration occurs there before the air is directed to annular channels surrounding the combustor. As is conventional, the compressor is provided with an inner compressor discharge inner barrel and a compressor discharge casing (CDC). The CDC interconnects the inner barrel and a first-stage nozzle.

A primary source of loss and turbulence in diffusers is vortex generation as flow enters the diffuser dump cavity. The diffuser dump cavity has the highest diffusion gradient, leading to vortex formation. As the fluid flow moves forward, the vortex grows and begins interacting with the upstream sections of the diffuser. Vortex growth elevates the fluid flow upstream of diffuser dump region and results in high loss and poor pre-diffuser and CDC performance.

As a result, there is a need for improved systems and apparatus that trap the vortex and arrest its growth in the dump cavity of the diffuser, thus reducing overall losses and ensuring robust diffuser performance.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a discharge diffuser that includes: a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity; an inner diffuser wall that defines an inner radial flowpath of the upstream section; and an outer diffuser wall that defines an outer radial flowpath of the upstream section; wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.

The present application further describes a discharge diffuser that includes: a forward section configured to direct compressor discharge from the compressor to a dump cavity; wherein: the forward section includes an inner diffuser wall and an outer diffuser wall, the outer diffuser wall flaring outwardly to define a widening flowpath therethrough; the dump cavity comprises a region of increased volume positioned downstream of the upstream section, the dump cavity being configured to surround at least a portion of a combustor; and at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step, the overhanging step including a step wall that, from the aft lip, slants radially inward and in an upstream direction so that the step wall undercuts a portion of the inner diffuser wall.

These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an exemplary discharge diffuser for a compressor in a combustion turbine engine that includes a vortex trap or over hanging step according to an embodiment of the present application;

FIG. 2 illustrates an exemplary discharge diffuser that includes a vortex trap or overhanging step according to an alternative embodiment of the present application;

FIG. 3 depicts exemplary dimensions of the various parts of the a vortex trap or overhanging step according to an exemplary embodiment of the present application;

FIG. 4 illustrates a fluid flow pattern within a conventional diffuser; and

FIG. 5 illustrates a fluid flow pattern within the discharge diffuser having a vortex trap or overhanging step according to an exemplary embodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

As an initial matter, to communicate clearly the invention of the current application, it may be necessary to select terminology that refers to and describes certain parts or machine components of a combustion turbine engine. Whenever possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. However, it is meant that any such terminology be given a broad meaning and not narrowly construed such that the meaning intended herein and the scope of the appended claims is unreasonably restricted. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different terms. In addition, what may be described herein as a single part may include and be referenced in another context as consisting of several component parts, or, what may be described herein as including multiple component parts may be fashioned into and, in some cases, referred to as a single part. As such, in understanding the scope of the invention described herein, attention should not only be paid to the terminology and description provided, but also to the structure, configuration, function, and/or usage of the component, as provided herein.

Further, as used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the turbine. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The terms “aft” and “forward” may be used to describe relative position within the turbine engine. It will be appreciated that the compressor is generally referred to as residing on the “forward” side of the turbine engine while the turbine section resides on the “aft” side. Accordingly, as used herein, “forward” describes a position closer to the compressor and “aft” describes a position closer to the turbine. The term “radial” refers to movement or position perpendicular to an axis. It is often required to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis.

FIG. 1 illustrates an exemplary compressor discharge diffuser 100 in a combustion turbine engine that includes a vortex trap or overhanging step according to an exemplary embodiment of the present application. The discharge diffuser 100 may direct compressed fluid from a compressor (not shown) to a combustor (not shown). In general, air in the turbine engine leaves the compressor with relatively high velocity and enters the diffuser 100, where it is then decelerated.

As shown by arrows in FIG. 1, the compressed fluid initially enters a forward section 101 of the discharge diffuser 100. The forward section 101 may include an inner diffuser wall 102 and an outer diffuser wall 104. It will be appreciated that the outer diffuser wall 104 flares outwardly such that the diffuser walls 102, 104 define a widening flow path through the forward section 101, which decelerates the incoming compressed air. Further, an annular splitter vane 105 may be included (as shown). The splitter vane 105 splits the forward section 101 of the discharge diffuser 100 into two passages—a first passage 106 and a second passage 108, which direct the compressor discharge to a dump cavity 110. (Note that only a portion of the dump cavity 110 is shown in FIGS. 1 through 3, whereas additional areas of the dump cavity 110 are shown in FIGS. 4 and 5). In certain implementations of the disclosure, the discharge diffuser 100 may include any number of splitter vanes or, alternatively, may include a single widening annular passage without splitter vanes.

Generally, the discharge diffuser 101 includes a dump cavity 110, which receives airflow from the forward section 101 (shown by arrows). It will be appreciated that within the dump cavity 110, air is directed into the annular channels surrounding the combustor. FIG. 1 shows the dump cavity 110 as a region of increased volume that is generally positioned downstream of the aft termination points of the inner diffuser wall 102 and the outer diffuser wall 104. The dump cavity 110 may include an inner cavity wall 112 that defines an inner radial boundary of the dump cavity 110 and, as stated, the dump cavity 110 may surround at least a portion of the combustor. The dump cavity 110 has a substantially high diffusion gradient, which, in operation, typically leads to the formation of a vortex or vortices (not shown). It will be appreciated by those of ordinary skill in the art that the formation of such vortices is a primary source of loss and turbulence, which negatively impact the efficiency of the engine. Typically, as the fluid flow moves downstream, the vortices grow and begin interacting with the upstream section 101 of the discharge diffuser 100, causing further efficiency losses.

The inner diffuser wall 102 terminates at an aft lip 113. As used herein, the aft lip 113 is the downstream or aft termination point of the inner diffuser wall 102, as indicated in FIGS. 1 and 2. In some embodiments, the inner diffuser wall 102 may include a transition step 116 that is positioned just forward of the aft lip 113, as shown. It will be appreciated that the aft lip 113 marks the transition point from the forward section 101 to the dump cavity 110 of the discharge diffuser 100. Conventional design, as shown in FIG. 4, provides a radial step at this location, with the step having a step wall that is substantially aligned with the radial direction.

According to embodiments of the present application, the discharge diffuser 100 includes an overhanging step 116, which, as discussed more below, serves to minimize or trap or arrest the growth of vortices in this region. The overhanging step 116 generally includes a step wall 118 that slants radially inward and in an upstream direction, thereby undercutting an aft portion of the inner cavity wall 112, as shown in the cross-sectional views of FIGS. 1 through 3. More specifically, the overhanging step 116 includes a step wall 118 that, from a beginning point at the aft lip 113 of the inner diffuser wall 102, slants in a direction that includes both an inboard directional component and an axial-upstream directional component. At one end, the step wall 118 connects to the inner diffuser wall 102 and, at the other end, connects to the inner cavity wall 112 at a forward edge (a location that is referred to herein as the dump cavity forward edge 119). It will be appreciated that, according to embodiments of the present application, the axial position of the dump cavity forward edge 119 is forward of the axial position of the aft lip 113. Of course, it is this configuration that creates the overhanging step 116, which, in turn, produces the flow dynamics that reduce the formation of vortices through the diffuser 100 during operation of the engine.

The step wall 118, as shown, may be planar, and, in cross-section, generally forms an angle 306 with a radial reference line, which is specifically illustrated in FIG. 3. As used herein, this angle will be referred to as the step wall angle 306. Conventionally, as stated, the step wall 118 is aligned with the radial reference line and, thus, the step wall angle 306 is approximately 0°. In other conventional arrangements (not shown), the step wall 118 forms a positive angle with the radial reference line, which, as used herein, refers to a configuration wherein the step wall 118 slants inward radially in the aft direction. As taught in the present application, however, the step wall 118 creates a negative angle with the radial reference line, which, as stated, creates an overhang or undercut. It has been discovered that configurations having certain step wall angles 306 or step wall angles 306 within a certain range provide enhanced performance. For example, in one preferred embodiment, the step wall angle 306 comprises a range between approximately −20° and −60°. More preferably, the step wall angle 306 comprises a range between approximately −30° and −50°. In some applications, an ideal step wall angle 306 comprises approximately 40°. As discussed in more detail below, the slant of the step wall 118 forms a vortex trap that arrests the growth of vortices and prevents the vortices from interacting with the fluid in the forward section 101 of the diffuser 100.

The aft lip 113 of the inner diffuser wall 102 may include several preferred configurations. In one configuration, as shown in FIG. 1, the aft lip 113 may have a smooth, rounded edge. In another preferred embodiment, as shown in FIG. 2, the aft lip 113 may have a sharp edge. In yet another preferred embodiment, as FIG. 3 shows, the aft lip 113 includes a flat surface, aligned in a substantially radial direction. These aft lip 113 alternatives have been proven effective at trapping vortices and reducing aerodynamic losses. While these described configurations for the aft lip 113 represent preferred embodiments, it will be appreciated that other configurations are possible.

In a preferred embodiment, the shape of the connection made between the step wall 118 and the inner cavity wall 112, as shown, includes a rounded, fillet region. As will be appreciated, this may prevent stress concentrations. Other configurations are also possible.

Further, it has been discovered through experimentation and computer modeling of flow patterns that certain dimensions are particularly more effective at controlling or limiting vortex formation than others. FIG. 3 assists in describing the exemplary dimensions of the various parts of an exemplary vortex trap 300 within the diffuser 100. For example, the radial height 312 of the overhanging step 116 may be between approximately 4 and 6 inches. More preferably, this radial height 312 may be approximately 4.4 inches. In some embodiments, the distance 302 between the transition step 114 and the aft lip 113 may be approximately 3.5 to 4.5 inches. More preferably, this distance 302 may be about 4 inches. In some embodiments, the height 304 of the flat edge of the aft lip 113 (see FIG. 3) may be between approximately 0 and 1 inches. More preferably, this height 304 may be approximately 0.5 inches. In some embodiments, the radius 308 of the arc formed between the step wall 118 and the inner cavity wall 112 may be between approximately 0.5 and 2 inches. More preferably, this radius 308 may be approximately 1 inch. Further, the height 310 of the transition step 114 may be between approximately 0.2 and 1 inches. More preferably, this height 310 may be around 0.5 inches. The above dimensions are optimized for minimizing overall losses due to vortex (not shown) growth and limiting vortex interaction with upstream fluid flow. It will be appreciated that these dimensions may be altered depending on the application and that they represent only a preferred method of practice.

FIG. 4 illustrates a fluid flow pattern within a conventional diffuser 400 and experimental results of same. The conventional diffuser 400 includes the first passage 106 and the second passage 108 through which the compressed fluid travels to the dump cavity 110, as shown by arrows. A step 402, which has a step wall oriented substantially in the radial direction, connects the inner diffuser wall 102 to the inner cavity wall 112 of the dump cavity 110, which is inboard in relation to the inner diffuser wall 102. The dump cavity 110 has the highest diffusion gradient, leading to vortex generation. A vortex 404 (which is represented by the shaded region) forms in proximity to the step 402 as fluid enters the dump cavity 110. The vortex 404 grows as the fluid moves downstream and begins interacting with the fluid in the forward section of the conventional diffuser 400. Fluid flow reversal in the dump cavity 110 climbs the step 402, which is a substantially vertical wall, and consequently, interacts with the upstream flow and aids to the further growth of the vortex 404. The interaction can be seen in FIG. 4, where the fluid is shown entering the second passage 108. This growth in the vortex 404 elevates the flow upstream of the dump cavity 110, leading to heavy loss and poor pre-diffuser and CDC performance.

FIG. 5 depicts a fluid flow pattern within the diffuser 100 according to an embodiment of the present application and experimental results of same. As discussed, the first leg 118 may slant radially inward and in an upstream direction so that the first leg 118 undercuts a portion of the inner diffuser wall 102. Further, the aft lip 113 may have an axial position that is aft relative to the axial position of the dump cavity forward edge 119. FIG. 5 shows a mitigated vortex 502 formed in close proximity to the step wall 118. The slant of the step wall 118 creates a vortex trap in the dump cavity 110, arresting the growth of the mitigated vortex 502 and preventing its interaction with the forward section 101 of the diffuser 100. FIG. 5 shows the mitigated vortex 502 being significantly disengaged from the second passage 108, as compared to the vortex 404 in FIG. 4, which has significant interaction with the second passage 108. This comparison illustrates the manner in which the present design of the diffuser 100 may prevent the growth of the mitigated vortex 502 and may substantially disengage the mitigated vortex 502 from the upstream fluid flow.

It will be appreciated that the design of the diffuser 100 also facilitates uniform flow distribution across a transition piece 504 and prevents the formation of hot spots. The resulting flow field reduces overall losses and improves the diffuser 100 performance. Further, containment of the mitigated vortex 502 relieves the stringent need of having a uniform flow profile at the compressor, without negatively affecting performance. The reduced losses in the CDC may also allow a higher margin of loss during compressor or combustor design, providing significant performance and financial benefit.

Table 1 compares the performance of the conventional diffuser 400 with that of the diffuser 100. Four scenarios are considered, having different leakage levels set at the fourteenth stator (S14) of the compressor, the leak being between the airfoil at S14 and the CDC. 0.3% leak at S14 is the design point for the present example. The pressure loss is measured according to the following equation 1:

$\begin{matrix} {\frac{DPt}{Pt} = \left( \frac{{{Pressure}\mspace{14mu} {at}\mspace{14mu} {diffuser}\mspace{14mu} {input}} - {{Pressure}\mspace{14mu} {at}\mspace{14mu} {diffuser}\mspace{14mu} {output}}}{{Pressure}\mspace{14mu} {at}\mspace{14mu} {diffuser}\mspace{14mu} {input}} \right)} & (1) \end{matrix}$

TABLE 1 DPt/Pt for S14 Leak conventional diffuser DPt/Pt for diffuser 100 (%) 400 (%) (%) 0.1 1.17 1.16 0.3 1.13 0.99 (design point) 0.4 1.19 1.03 0.8 1.42 1.3

It should be noted that, typically, significant effort is invested in uniformly maintaining such low levels of leakage. The reduced losses in the diffuser 100 may impart some flexibility during compressor or combustor design and may further relax the stringent requirements for maintaining leakage levels.

Table 1 shows that the diffuser 100 lowers the pressure loss due to vortex growth compared to the conventional diffuser 400. It should be noted that the claimed diffuser design provides robust performance not only at design point, but also across various operating conditions. Thus, the diffuser 100, according to the embodiments of the present disclosure, restricts vortex growth and limits upstream flow interaction with the vortex, leading to substantial improvements in diffuser and CDC performance.

As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof. 

1. A discharge diffuser in a combustion turbine engine that includes a compressor, a combustor and a turbine, the discharge diffuser comprising: a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity; an inner diffuser wall that defines an inner radial flowpath of the upstream section; and an outer diffuser wall that defines an outer radial flowpath of the upstream section; wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.
 2. The discharge diffuser according to claim 1, wherein the outer diffuser wall flares outwardly such that the inner diffuser wall and the outer diffuser wall define a widening flowpath, and the aft lip comprises the downstream termination point of the inner diffuser wall.
 3. The discharge diffuser according to claim 2, wherein the dump cavity comprises a region of increased volume positioned downstream of the flared inner and outer diffuser walls of the upstream section, and wherein the dump cavity is configured to surround at least a portion of the combustor.
 4. The discharge diffuser according to claim 1, wherein the overhanging step comprises a step wall that extends from the aft lip of the forward section to an inner cavity wall of the dump cavity, the inner cavity wall comprising an inner radial boundary of the dump cavity.
 5. The discharge diffuser according to claim 4, wherein the step wall comprises a radial step that, from a beginning point at the aft lip of the inner diffuser wall, slants in a direction that includes both an inboard directional component and an axial-upstream directional component.
 6. The discharge diffuser according to claim 4, wherein the overhanging step comprises a radial step that, from the aft lip, slants radially inward and in an upstream direction so that the radial step undercuts a portion of the inner diffuser wall.
 7. The discharge diffuser according to claim 1, wherein: the dump cavity comprises an inner cavity wall that defines an inner radial boundary of the dump cavity; and the overhanging step includes a step wall that connects the inner diffuser wall to the inner cavity wall.
 8. The discharge diffuser according to claim 7, wherein the inner cavity wall comprises a position that is inboard in relation to the inner diffuser wall; and wherein the radial height of the overhanging step comprises the distance by which the inner cavity wall is inboard of the inner diffuser wall.
 9. The discharge diffuser according to claim 8, wherein the step wall, at one end, connects to the inner diffuser wall at the aft lip and, at the other end, connects to the inner cavity wall at a dump cavity forward edge.
 10. The discharge diffuser according to claim 9, wherein the overhanging step is configured such that the aft lip comprises an axial position that is aft relative to the axial position of the dump cavity forward edge.
 11. The discharge diffuser according to claim 10, wherein: the step wall comprises a substantially planar shape; a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and the overhanging step is configured such that the step wall angle comprises a range of between 20 and 60 degrees.
 12. The discharge diffuser according to claim 10, wherein: the step wall comprises a substantially planar shape; a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and the overhanging step is configured such that the step wall angle comprises a range of between 30 and 50 degrees.
 13. The discharge diffuser according to claim 10, wherein: the step wall comprises a substantially planar shape; a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and the overhanging step is configured such that the step wall angle comprises approximately 40 degrees.
 14. The discharge diffuser according to claim 10, wherein the aft lip comprises one of a rounded edge, a sharp edge, and a radially aligned flat edge; and wherein the dump cavity forward edge comprises a filleted edge.
 15. The discharge diffuser according to claim 10, wherein the radial height of the overhanging step comprises 4 to 6 inches.
 16. The discharge diffuser according to claim 10, further comprising a transition step located on the inner diffuser wall; wherein the distance between a transition step located on the inner diffuser wall and the aft lip comprises 3.5 to 4.5 inches; and wherein the radial height of the transition step comprises approximately 0.5 inches.
 17. A discharge diffuser for a combustion turbine engine that includes a compressor, a combustor and a turbine, the discharge diffuser comprising: a forward section configured to direct compressor discharge from the compressor to a dump cavity; wherein: the forward section includes an inner diffuser wall and an outer diffuser wall, the outer diffuser wall flaring outwardly to define a widening flowpath therethrough; the dump cavity comprises a region of increased volume positioned downstream of the upstream section, the dump cavity being configured to surround at least a portion of a combustor; and at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step, the overhanging step including a step wall that, from the aft lip, slants radially inward and in an upstream direction so that the step wall undercuts a portion of the inner diffuser wall.
 18. The discharge diffuser according to claim 17, wherein: the dump cavity comprises an inner dump cavity wall that defines an inner radial boundary of the dump cavity; and the step wall connects the inner diffuser wall to the inner cavity wall, the inner dump cavity wall comprising a position that is inboard in relation to the inner diffuser wall.
 19. The discharge diffuser according to claim 18, wherein: the step wall, at one end, connects to the inner diffuser wall at the aft lip and, at the other end, connects to the inner cavity wall at a dump cavity forward edge; and the overhanging step is configured such that the aft lip comprises an axial position that is aft relative to the axial position of the dump cavity forward edge.
 20. The discharge diffuser according to claim 18, wherein: the step wall comprises a substantially planar shape; a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and the overhanging step is configured such that the step wall angle comprises a range of between 30 and 50 degrees. 